Begun in 1173 as the third and final structure of the city's cathedral complex, it was designed to stand 185 ft (56 m) high. Work was suspended several times as engineers sought solutions; the tower, still leaning, was completed in the 14th century. Subsiding at the rate of 0.03 in (1.2 mm) a year, the structure was in danger of collapse, and in 1990 it was closed as engineers undertook a strengthening project that decreased the lean by 17 in (44 cm) to about 13.5 ft (4.1 m). The work was completed in May 2001. Source: http://concise.britannica.com/ebc/article?eu=395204 *** 'The Tower of Pisa was designed as a bell tower and to brag to Pisa's nemesis, the city of Florence. When the infamous tilt was discovered during construction in 1178, the builders decided to continue with the project regardless. The cause of the tilt is commonly attributed to unstable soil under the tower, although some historians believe that the tilt was actually part of the original architect's design. There have been many attempts over the centuries to remove or reduce the southerly tilt; the most successful was also the most recent. In 1990, an Italian government-appointed special commission determined that the tower was no longer safe for tourists, closed it off, and started devising ways to make the building safer. John Burland, a professor of soil mechanics, came up with the system of removing soil from the north side in order to make the building settle back into the ground and thus reduce the tilt. This worked and the tower was reopened to tourism in 2001.' Source: http://architecture.about.com/library/blleaningtowerofpisa.htm